1. Field of the Invention
The invention relates to a method for calculating a height map of a sample having a body of a transparent material having a refractive index with an inclined surface, the body being provided on an underlying surface extending laterally from underneath the body.
2. Description of Related Art
A height map of a body may be measured with an optical profiler. The optical profiler may, for example, be a broadband interferometer, e.g. a Mirau, Michelson and/or Linnik interferometer apparatus.
Such apparatus for determining a height map of a surface may have:
a broadband illuminator for providing a broadband illumination beam;
a beam splitter for splitting the illumination beam in a reference beam for reflection on a reference reflector and a measurement beam for reflection on the surface;
a detector for receiving an interference radiation intensity from the reflected reference beam from the reference reflector and the reflected measurement beam from the surface;
a scanning means for changing the distance between the surface and the apparatus; and,
a processing means for receiving a signal representing the interference radiation intensity received on the detector from the detector and a distance signal from the scanning means and combining both to a height map.
The interference radiation intensity received on the detector has a maximum value when the optical path of the reference beam is equal to the optical path of the measurement beam. The scanning means may change the distance between the test surface and the apparatus with a few hundreds of microns around this maximum value to determine a height map of the surface.
The apparatus may have an objective to image the reflected measurement beam from the surface on the detector. The last lens element LE of the objective (see FIG. 4) of the optical profiler may have a limited numerical aperture and therefore if the surface SF is inclined the reflected measurement beam RM from the inclined surface may be reflected outside the numerical aperture of the objective (see ON) and the apparatus can not measure the height map. In this patent application an inclined surface is defined as a surface with an inclination such that the reflected measurement beam is reflected outside the numerical aperture of the objective of the optical profiler and a normal height map cannot be measured with the optical profiler.